The present invention, in some embodiments thereof, relates to methods of diagnosing and treating motor neuron diseases and, more particularly, but not exclusively, to Amyotrophic Lateral Sclerosis (ALS).
Motor neuron diseases (MND) belong to a group of neurological disorders attributed to the destruction of motor neurons of the central nervous system and degenerative changes in the motor neuron pathway. Such diseases are different from other neurodegenerative diseases including Parkinson's disease, Alzheimer's disease, olivopontocerebellar atrophy, etc., which are caused by the destruction of neurons other than motor neurons. Typically, MNDs are progressive, degenerative disorders that affect nerves in the upper or lower parts of the body. Generally, MNDs strike in middle age. Symptoms may include difficulty swallowing, limb weakness, slurred speech, impaired gait, facial weakness and muscle cramps. Respiration may be affected in the later stages of these diseases. The cause(s) of most MNDs are not known, but environmental, toxic, viral or genetic factors are all suspects.
Motor neurons, including upper motor neurons and lower motor neurons, affect voluntary muscles, stimulating them to contract. Upper motor neurons originate in the cerebral cortex and send fibers through the brainstem and the spinal cord, and are involved in controlling lower motor neurons. Lower motor neurons are located in the brainstem and the spinal cord and send fibers out to muscles. Lower motor neuron diseases are diseases involving lower motor neuron degeneration. When a lower motor neuron degenerates, the muscle fibers it normally activates become disconnected and do not contract, causing muscle weakness and diminished reflexes. Loss of either type of neurons results in weakness, muscle atrophy (wasting) and painless weakness are the clinical hallmarks of MND.
Amyotrophic Lateral Sclerosis (ALS) is a fatal motor neuron disease characterized by a loss of pyramidal cells in the cerebral motor cortex (i.e., giant Betz cells), anterior spinal motor neurons and brain stem motor neurons, and degeneration thereof into pyramidal cells. ALS shows, from a clinical aspect, both upper motor neurons and lower motor neurons signs, and shows rapid clinical deterioration after onset of the disease, thus leading to death within a few years.
Like many other motor neuron diseases, only a small percentage (about 10%-15%) of ALS is inherited. Genetic epidemiology of ALS has revealed at least six chromosome locations accountable for the inheritance of disease (ALS1 to ALS6). Among these, three genes have been identified. The first was identified in 1993 as the cytosolic Cu/Zn superoxide dismutase (SOD-1) gene that accounts for 20% of the autosomal dominant form of ALS (Rosen et al., 1993, Nature, 1993 Mar. 4; 362(6415):59-62). The discovery of this primary genetic cause of ALS has provided a basis for generating mouse models for this disease. These models are useful for testing therapies that might aid in the treatment of ALS.
The second was named as Alsin, a potential guanine-nucleotide exchange factor (GEF) responsible for the juvenile recessive form of ALS. The third is ALS4 that encodes for a DNA/RNA helicase domain containing protein called Senataxin identified to be linked to the autosomal dominant form of juvenile ALS. Most recently, a mutation in the vesicle associated membrane protein/synaptobrevin associated membrane protein B (VAPB) in a new locus called ALS8, was reported to be associated with an atypical form of ALS.
Riluzole is the sole drug approved for ALS in U.S. and Japan. Riluzole was originally developed as an anticonvulsant inhibiting glutamate release and has been reported in several clinical trials to exhibit only slight efficacy for the survival of ALS patients (Rowland L P and Shneider N A, 2001, N Engl J Med, 344, 1688-1700; and Turner M R and Parton M J, 2001, Semin Neurol 21: 167-175).
Micro-RNAs (also known as miRNAs) are 20- to 24-nucleotide (nt) RNA molecule members of the family of non-coding small RNAs. Micro-RNAs were identified in mammals, worms, fruit flies and plants and are believed to regulate the stability of their target messenger RNA (mRNA) transcripts in a tissue- and cell type-specific manner. Principally, micro-RNAs regulate RNA stability by either binding to the 3′-untranslated region (3′-UTR) of target mRNAs and thereby suppressing translation, or in similar manner to siRNAs, binding to and destroying target transcripts in a sequence-dependent manner.
Micro-RNAs were found to be involved in various cell differentiation pathways. For example, miR-181, was found to be preferentially expressed in the B-lymphoid cells and its ectopic expression in hematopoietic stem/progenitor cells led to an increased fraction of B-lineage cells in vitro and in vivo. In addition, miR-23 was shown to be present in differentiated, but not undifferentiated, human neural progenitor NT2 cells and to regulate a transcriptional repressor in such cells. Other researchers have identified the generation of intron-derived micro-RNA-like molecules (Id-micro-RNA) from these regions as a tool for analysis of gene function and development of gene-specific therapeutics, and predicted possible applications including major gene modulation systems for developmental regulation, intracellular immunity, heterochromatin inactivation, and genomic evolution in eukaryotes (Lin and Ying, 2004b).
Micro-RNAs have been implicated in various neurological diseases such as Fragile X syndrome, spinal muscular atrophy (SMA), early onset parkinsonism (Waisman syndrome) and X-linked mental retaradation (MRX3), as well as various cancers and precancerous conditions such as Wilm's tumor, testicular germ cell tumor, chronic lymphocytic leukemia (CLL), B cell leukemia, precancerous and neoplastic colorectal tissues and Burkkit's lymphoma [reviewed in Gong H, et al., 2004, Medical Research Reviews, Published online in Wiley InterScience (www.intersciencedotwileydotcom)].
U.S. Patent Application 20060247193 teaches administration of over 100 miRNAs for the treatment of MNDs including ALS.
U.S. Patent Application 20090246136 teaches administration of miR-206 and/or miR-1 for the treatment of MNDs including ALS.
Figlewicz et al [Human Molecular Genetics, Volume 3, 1994] teaches that variants of the heavy neurofilament subunit are associated with the development of ALS.
Additional relevant background art includes U.S. Patent Application 20080176766.